Area of compound shapes — Notes & Worked Examples Show / Hide
Explanation:
A compound (composite) shape is made up of two or more simple shapes joined together. To find its area, draw a dotted line to split it into rectangles or triangles, work out any missing side lengths first by comparing parallel horizontal and vertical sides, and then add the separate areas together.
Remember the key area formulas: Rectangle = length × width, and Triangle = 12 × base × perpendicular height. For shaded region questions, calculate the outer area minus the unshaded inner area.
Example 1: An L-shape has total width 10 cm, total height 8 cm, top width 4 cm, and right height 3 cm. Find its area.
Example 2: A pentagon has a 6 m by 4 m rectangular base and a triangle on top. Total height is 7 m. Find the area.
Worked Solution & Answer
51 cm2
Worked Solution & Answer
Worked Solution & Answer
Area of kite = ½ × 6 × 4 = 12 cm² M2
draw a 4 cm by 3 cm rectangle A1
Worked Solution & Answer
Area of cut-out hole = 2 × 3 = 6 cm2 M1
Shaded area = 20 - 6 = 14 cm2
Percentage shaded = 1420 × 100% = 70%. A1
The area of the shape is 91.8 cm2
Worked Solution & Answer
⇒ 11x = 52.8 M1
⇒ x = 4.8 A1
Worked Solution & Answer
Area of 1 tile = 4 × 3 = 12 cm² M1
Total area = 4 × 12 = 48 cm². A1
The stage is made up of a rectangle and an isosceles triangle.
She needs to buy enough tins of varnish to cover the stage with one coat of varnish.
Each tin of varnish covers an area of 4 m2
Work out the smallest number of tins of varnish that Yuko needs to buy.
Show your working clearly.
Worked Solution & Answer
Triangle area = ½ × 6 × 3 = 9 m² M1
Total area = 48 + 9 = 57 m² M1
57 ÷ 4 = 14.25 ⇒ 15 tins A1
Work out the area.
16 (b) Zak wants to work out the area of this triangle.
Here is his working.
12 × 8 = 96 cm2
What is wrong with his method?
Here is his working.
12 × 8 = 96 cm2
What is wrong with his method? [1 mark]
Worked Solution & Answer
Top rectangle: 9 × 2 = 18 cm2 M1
Bottom rectangle: 4 × (8 - 2) = 4 × 6 = 24 cm2
Total area = 18 + 24 = 42 cm2 A1
The formula for the area of a triangle is 12 × base × perpendicular height , so he needed to divide by 2. B1
Petra is going to cover the floor with paint.
Petra has 3 tins of paint.
There are 2.5 litres of paint in each tin.
Petra thinks 1 litre of paint will cover 10 m2 of floor.
You must show all your working. [4 marks]
You must give a reason for your answer. [1 mark]
Worked Solution & Answer
Paint = 3 × 2.5 × 10 = 75 m² > 68 m², so Yes A1